Centrifugal pump with slip coupling



March 18, 1969 s. ENGLESSON CENTRIFUGAL PUMP WITH SLIP COUPLING SheetFiled March 20, 196'? INVENTOR! S'lnn E17/03901, 37M. Mn-nl,

M3 orney March 18, 1969 s. ENGLEssoN 3,433,162

CNTRIFUGAL PUMP WITH SLIP COUPLING Filed March 2o, 1967 sheet 2 of sMarch 18, 1969 s, ENGLESSON 3,433,162

CENTRIFUGAL PUMP WITH SLIP COUPLING Filed March 20, 1967 sheet '3 of 5Figlia Discharge against a constant pressure head in the pipe systemirrespective of the discharge from same, the pressure at the suctionbeing variable Pressure at suction side Pressure head in the ipe systemFiglib Pressure head in the pipe system Mu Ada/my March 18, 1969 s.ENGLEssoN 3,433,162

CENTRIFUGAL PUMP WITH SLIP COUPLING' Filed March 2o, 19e? sheet 4 of 5Fig. 5a Discharge against a constant pressure head in the pipe systemirrespective of the discharge from same, the pressure at' the suctionside being constant.

H Constant level const.

F i g. 5 b H H const.\

n1 I"2 nmax O Q Q Q No discharge from 1 2 max pipe system INVENTOR:

aI/MA M,

March 18, 1969 s. ENGLEssoN 3,433,162

CENTRIFUGAL PUMP WITH SLIP COUPLING Filed March 2o, 1967 sheet 5 of sReshaping of the pump characteristic and protection of the motor againstoverload by torque limitation Mv max The motor speed is assumed to beconstant IN VEN TOR r S'fxe/J Eng/essen,

United States Patent O 4,865/ 66 U.S. Cl. 103-87 2 Claims Int. Cl. F04d13/04; F04!) 49/02 ABSTRACT OF THE DISCLOSURE A membrane-actuatedthrottle valve is provided between the discharge and the suction side ofa slip-coupling connecting the impeller of a centrifugal pump to thedrive motor shaft.

The present invention refers to a centrifugal pump comprising aslip-coupling connected between the motor and the pump, which deviceprovides the possibility of achieving a certain speed regulation byslippage. The slippage, however, is a loss which is proportional to thedifference in revolutions which is converted into heat which must bedissipated by cooling.

The application thus relates to a centrifugal pump comprising animpeller arranged in a fluid chamber for the pumped uid and a drivingmotor for said impeller arranged outside the pumped duid. Theslip-coupling connecting the impeller to the driving motor is located insaid tluid chamber.

lt is an object of the present invention to further increase thepossibilities of controlling the impeller speed by means of aslip-coupling, the invention being essentially characterized in that acontrollable throttle valve is provided between the discharge and thesuction side of the coupling.

A centrifugal pump provided with said device makes it for instancepossible to maintain a constant pressure in a pipe system irrespectiveof the discharge from the system and to a certain extent evenirrespective of the pressure at the suction side of the pump. Thispossibility can be provided by a further development of the inventionwhich consists in that the controllable throttle valve is controlled bya liquid pressure at the discharged side of the centrifugal pump.

Another operation possibility when using the pump according to thepresent invention consists in that it is even possible to provide aconstant pressure in the pipe system irrespectve of the discharge fromsaid system, the pressure at the suction side of the pump remainingconstant. To that purpose, according to a further modification of theinvention, the controllable throttle valve is arranged to be controledby a pressure-sensitive means preferably connected to the discharge sideofthe pump.

A further operation possibility provided by the invention includes theuse of the slip-coupling for limiting the capacity in sewage-waterpumps, particularly submersible pumps, having a maximum free passagethrough the pump impeller. According to a further embodiment of theinvention an adjustable throttle valve is to that purpose providedbetween the suction side of the discharge side of the slip-coupling,said throttle valve responding to a spring set for a determined torqueof the pump shaft. Said adjustable spring-biased throttle valve may beeither connected in parrallel with the controllable throttle valve or beconstituted by said controllable throttle valve.

For actuating the controllable valve a diaphragm-actuated stem isprovided which is tted in an axial recess in the impeller drive shaft,said valve being preferably constituted by a slide arranged for axialreciprocating movement in said recess.

The invention will be more particularly described hereinafter withreference to the accompanying drawings, in which:

FIG. 1 illustrates a pumping unit comprising a pump impeller wth abuilt-in slip-coupling,

FIG. 2 is a top plan view of the slip-coupling partly in section,

FIG. 3 is a vertical section through a slip-coupling,

FIGS. 4a and 4b are graphs illustrating the operation when the pumpdischarges against a constant pressure head in the system andirrespective of the magnitude of the discharge from the system, thepressure on the suction side being variable,

FIGS. 5a and 5b are a diagramm and a graph, respectively, illustratingthe operation when pumping against a constant pressure head in thesystem irrespective of the` discharge from the system, the pressure onthe suction side being constant, and

FIG. 6 is a graph illustrating the operation when the pumpcharacteristic is modified and a protection against overload is achievedby limiting the torque in the slipcoupling.

FlG. l shows a pumping unit comprising a pump with a pump casing 1, animpeller 2 and an end plate 3. The stator casing 4 of the motor isflanged onto the end plate 3, 5 being the hollow pump shaft. A stem 6shown in dashed lines is titted inside the hollow shaft for axialdisplacement upwards and downwards, said stem being actuated by amembrane 7 against the action of a spring 8. The membrane is arranged ina pressure chamber 9 to which pressure liquid from the discharge side 11of the pump can be conveyed Via a duct 10.

ln the fluid chamber 12 of the pump casing is provided a slip-couplingwith a casing 13 tted to the impeller 2 and a rotor 14 secured to themotor shaft 5. The rotor 14 of the slip-coupling is provided with blades15 arranged for sliding radially outwards preferably under springaction, which blades transmit the rotational movement of the impeller tothe transmission medium, preferably oil, contained in the slip-couplingcasing 13.

The slip-coupling casing is also provided with suction channels 16 anddischarge channels 17 which via ports 13 and 19, respectively, providedin spaced relationship along the pump shaft periphery are communicatingwith the inside of the pump shaft and corresponding recesses provided inthe control slide 20 of the valve, said slide moving axially togetherwith the stem 6.

FIGS. 2 and 3 are detail views of the slip-coupling. FIG. 3 is a sectionalong the lines A-A in FIG. 2. The same reference numerals as in FIG. 1have been used. The casing of the slip-coupling has been shown with asomewhat exaggerated elliptic shape, it being understood that in realitythe ellipse is to be more circular since the oil volume between twoadjacent blades 15 may not vary during the passage of the blades fromthe suction side to the discharge side, if leaks 4between the blades andthe casing are to be avoided. The blades 15 are thrust outwards againstthe slip-coupling casing by springs 21. Ports 18, 19 are provided alongthe periphery of the pump shaft 5 4in order to ensure communicationbetween the channels 16, 17 and the inside of the pump shaft.

The slip-coupling operates as follows: The slip coupling rotor 14rotates together with a shaft 5 and the blades 15 convey the pressurefluid ahead of them from the suction channel 16 to the dischargedchannel 17. If the stem 6 and consequently the slide 20 are in theuppermost position, the throttle valve is entirely closed and nocommunication exists between the suction and the discharged side of theslip-coupling. The motor shaft is in that case firmly coupled to theimpeller. As soon as the pressure at the discharged side 11 of the pumpbecomes too high, the pumped fluid is forced upwardly through the duct10 into the pressure chamber l9 in the pressure controller on top of themembrane 7 and thrusts the stem 6 downward against the action of thespring 8 so that the valve slide 20 is moved to its lower position,whereby the throttle valve is open so that oil may pass from thedischarge side to the suction side of the slip-coupling. Depending uponhow large section of said channel is opened by the motion of the slide20, a larger or smaller part of the work supplied to the slip-couplingrotor is used for pumping oil through the channels of the slip-coupling.Slippage occurs in the slip-coupling and the impeller will thus rotateat a lower speed than the rotor shaft.

Various applications of the invention will be described below, referenceIbeing made to the graphs 4-6.

FIGS. 4a and 4b are graphs illustrating operating conditions where thepressure at the suction side is supposed to be variable but 'where inspite of that the pressure in the pipe system at the discharge side isto be kept constant irrespective of the discharge from the system. FIG.4a illustrates a boarder-line case where the available water pressure atthe suction side is equal to the pressure which is to be maintained inthe pipe system. In this case the pressure feeding pipe system issufliciently high and a pressure controller of the kind shown in FIG. lwill therefor adjust the slip-coupling so that slippage occurs; the-impeller is only to follow the liquid stream resulting from the waterpressure at the suction side without retarding it.

Should on the other hand the pressure at the suction side drop below thepressure head in the discharge pipe system, as illustrated in FIG. 4b,the pump will have to provide an additional pressure to the pressure ofthe 'water at the suction side in order to provide the required pressurehead in the discharge system. In that case the pressure head in the pipesystem will drop at lirst. As a result thereof the channels in theslip-coupling are closed by the slide 20 moving upward. The slippage inthe slipcoupling is thus reduced and a firmer coupling is achievedbetween the motor shaft and the impeller, whereby the pump is thus ableto provide the additional pressure head required. Depending upon the Howrate Q, Q1, Q2 or Qmax, respectively, discharged from the pipe system,the speed of the impeller will be adjusted to requirement by the slipcoupling.

FIGS. a and 5bV illustrate an applicat-ion example of the inventionunder operating conditions where a constant pressure is to 'bemaintained in the pipe system irrespective of the discharge from same,the pressure from the suction side remaining constant.

As appears from the figures pipe friction losses have been disregardedand for a constant pressure head in the pipe system, Hconst, one obtainsalong a horizontal line the design points corresponding to a certaindischarge Q2 or Qmax from the pipe system, which design points areindicated -by edges. An impeller speed n2 corresponds for instance to adischarge Q2 from the pipe system and an impeller speed nmax correspondsto a discharge Qmax from the pipe system. The control of the slippage ofthe slipcoupling is also in this case assumed to be achieved by apressure from the discharge side of the impeller which pressure, asdescribed above, adjusts the slide in the slip-coupling as required inorder to obtain the desired slippage.

With reference to the graph in FIG. 6, operation conditions will bedescribed in the case where one desires to reshape the pumpcharacteristic whereby a protection against motor overload is obtainedby limiting the torque transmitted by the slip-coupling. This type ofoperation is particularly appropriate when the power requirement ofsewage-water pumps having a maximized free passage through the impelleris to be limited.

1n centrifugal (pumps for sewageand waste-water the aim is to achieve amaximized free passage through the impeller and the casing volute. Idealconditions are achieved when the pump inlet and the impeller channelshave the same size so that all what comes in through the pump inlet alsomay pass through the whole pump. In other words, there is a free passagefor a ball, the diameter of which is equal to that of the lpump inlet.The pressure and iiow rate curve of the pump is then quite flat; the owrate increases rapidly and therewith also the driving power required onthe pump shaft when the counter-pressure decreases. This is inconvenientfor two reasons.

One of them is that a huge and expensive motor is required for drivingthe pump unit if the motor is to be sutiicient along the wholecharacteristic curve of the pump. The power consumption is high. Theother reason is that a very lar-ge quantity of water is discharged intothe pipe system, a quantity which may exceed the system capacity andthere is a risk for water rising up in the nearby draining gutters andthe like.

As shown in FIG. 6 the invention provides the possibility to limit theAflat part of the characteristic by limiting the impeller speed. By aprogressive reduction of the impeller speed it is thus possible to givethe characteristic a steaper or atter shape as desired.

A sewage-water pump usually exhausts water from a pit or collectingwell, in which the Water is allowed to rise up to a level of 1 meter forinstance. The pumps are then started automatically, usually one at atime, and exhaust the water until it reaches the lower level. As thewater level in the collecting well drops, the static head increases andthe flow rate decreases accordingly. With a very flat characteristiclike the one obtained with an impeller having a large free passage, thedifference between flow rate at the beginning and at the end of thepumping can be considerable. This leads also to a greater powerrequirement at the beginning of the pumping.

The speed control according to the invention provides the possibilitiesto make the characteristic within said area entirely vertical so thatthe flow rate discharged to the pipe system is uniform irrespective ofthe head variation.

The control impulses can be obtained from the power supplied to themotor, possibly from the motor current. The speed control can also beachieved by means of a slip-coupling whereby the latter is adjusted fora certain maximum torque. The invention may suitably be used also inconnection with purification plants having biologic strata or the like.In such plants it is important that sewage-water is supplied at aconstant ow rate. In this case the control impulses are provided by asuitable flow-rate meter.

Heavy concussions occuring in the pipes in connection with the stoppageof the pumps are also a problem which can be solved by means of theinvention. If the refluxvalve does not close entirely at the instant thewater velocity has dropped to zero after stopping the pump the liquidcolumn will mn backwards gaining in velocity and when the reflux-valvenally closes there occurs a Iwater hammer resulting in severe stresseson the piping and even noise. The invention provides a possibility toreduce the speed of the pump until the flow has stopped. i.e. until themanomatric head of the pump is equal to or somewhat lower than thestatic head and the pump is not stopped until this condition is reached.

The pump can also be started in the same way whereby a more progressivestart with a lower starting current is achieved.

The -graph in FIG. v6 illustrates how the slip coupling operates inorder to avoid motor overload. At the speed nm,X the pump discharges ata Iiiow rate QmaX whereby the motor consumes a power of n-max HP whichcorresponds to a maximum MV max. The slip coupling now starts operatingin that the spring-biased Valve in the coupling opens. Slippage occursand the pump shaft speed drops to n1 which corresponds to a dischargedow rate Q1. The motor output simultaneously drops to N1. At the instantwhen the slippage occurs the pump characteristie thus gets steeper inthat the characteristic is bent downward at a point corresponding toNmax.

Although the invention has been described in connection with theembodiment shown in the drawings, it is obvious that many alterations ormodications may be made within the scope of the appending claims.

What I claim is:

1. A centrifugal pump including a fluid pumping chamber, an impellerarranged in said fluid pumping chamber, a shaft in driving connectionwith said impeller, a motor driving said impeller by means of saidshaft, said motor being arranged outside the pumped fluid, and ahydrostatic slip-coupling arranged in said uid pumping chamber, saidslip-coupling being provided with a throttle valve between the dischargeand the suction side of the coupling, which valve is controlled by theliquid pressure at the discharge side of the centrifugal pump.

2. A centrifugal pump as claimed in claim 1, a nonrotat able stem beingtted in an axial recess in the impeller drive shaft, said valve beingactuated by means of said non-rotatable stem operated by said pressure.

References Cited UNITED STATES PATENTS 2,009,001 7/ 1935 Peterson.2,933,129 4/1960 Wright 103-35 XR 3,155,040 11/1964 Shurts et al. 103-35ROBERT M. WALKER, Primary Examiner.

U.S. Cl. X.R. 230-15

